Mazda first started talking about its diesel-like self-igniting SkyActiv-X gasoline engine back in January. Yet in March at the Geneva Motor Show, we just couldn't get any more info out of them, despite being very curious about how they plan to remove those crucial spark plugs from the system.

Now, almost five months later, Mazda's future powertrain plan is out, and as a complement to its electrification program, the company is hoping to perfect internal combustion using a revolutionary technology called the Homogeneous Charge Compression Ignition engine.

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Compared to the current Skyactiv-G generation, the Skyactiv-X is said to be 20-30 percent more efficient, achieving its numbers by using compression-ignition at lower loads. The Skyactiv-X will also be supercharged, and despite earlier reports, it retains its spark plugs for igniting the air-fuel mixture under higher loads like during warm up for full throttle running.

The theory is that while on the highway, the HCCI will use high compression to ignite like a diesel does, running a very lean mixture and reducing emissions. But once you step on it, the X switches back to being a regular supercharged Atkinson cycle gas engine, starting the ignition process with a spark before allowing the increased pressure to heat up the cylinder and ignite the rest of the mixture without further help.

Without knowing the engine's exact specifications, three main questions remain unanswered:

How can Mazda regulate temperatures to make sure ignition happens without creating engine knock at the other end?

How smoothly will the system switch from homogeneous charge compression ignition to spark and back?

Can the Miata stay naturally-aspirated?

In the meantime, here's Engineering Explained with Jason Fenske telling us more about Mazda's weapon X: